Really simple job to do.Start with the mast cheap enough from the dealers.

Only tool needed is an open ended 13mm spanner,
Start off by having an assistant switch on the radio so the mast goes up as far as it can.Then undo the top nut with the spanner.

It will look like this when undone.

Get your assistant to switch off the radio so the mast goes down about halfway then get them to switch it back on, so the mast goes back up,be ready to catch it as it comes out,Take note which way the teeth are facing on the plastic rod.(facing towards the rear on mine)

Your new mast is ready to install.Push the plastic rod into the hole with the teeth facing the rear of the car.

Get your assistant to switch off the radio,so you can push gently on the mast so it goes in and locates on the geared drive and starts to retract.When it goes in you can then start tightening the new nut up and then finish off with the 13mm spanner.